Generally, if dust continuously enters an optical disk drive, the dust adheres to an optical system of an optical head, in particular, an objective lens, and an amount of light emitted from the optical head is reduced progressively. When the amount of light is reduced progressively, amplitudes of a recording/reproducing signal as well as a focusing control signal and a tracking control signal for the objective lens deteriorate continuously, and finally the system fails, so that it becomes impossible to perform recording/reproduction. On this account, to ensure the reliability of the optical disk drive, it is necessary to take dust-proofing measures to prevent the entry of dust as much as possible, such as hermetically sealing the optical disk drive.
On the other hand, an optical disk device on which the optical disk drive is mounted is equipped with parts as sources of heat generation, such as a disk motor, an optical head transfer motor, a semiconductor laser mounted on the optical head, a drive circuit for driving these elements, and a power source.
When the optical disk drive is sealed hermetically for the purpose of the dust-proofing measures as described above, heat from the respective heat generation sources is unlikely to be transferred, and the heat remains to be accumulated there. In particular, in the case of the semiconductor laser, there is a correlation between an operating temperature environment and the lifetime, and the lifetime of the element is shortened when it is used at a high temperature. Accordingly, it is desirable that this element is operated in an environment of as low a temperature as possible. However, in a recording operation using the element with a high power, the heat generated from the element itself becomes high.
Moreover, due to the hermetically sealed optical disk drive, the heat is accumulated, and the temperature of the element is raised beyond a guaranteed temperature range of the element set in consideration of the lifetime. Consequently, to ensure a sufficient reliability of the device, it is indispensable to take measures to radiate the heat from the semiconductor laser.
As a solution to the conflicting problems of dust-proofing and heat-radiation measures, an optical disk sub-system device is proposed in JP 8(1996)-102180A, for example. The optical disk sub-system device includes an optical disk drive, a power source for driving the optical disk drive, and a cooler for cooling the inside of a housing. In the device, the housing internally is partitioned into a first chamber and a second chamber by a sill plate, and the first chamber in which the optical disk drive and the cooler are disposed is sealed hermetically, and the cooler forms an internal air circulation path.
According to this conventional example, since the first chamber is sealed hermetically, the optical disk drive disposed therein is free from an adverse effect due to dust. In addition, since the cooler circulates air in the first chamber, a temperature distribution in the first chamber gradually is made homogeneous, and a temperature of a semiconductor laser mounted on an optical head also is reduced.
However, in this configuration, the internal air circulation path is formed in the hermetically sealed first chamber so as to form an airflow throughout the first chamber. While this airflow has an effect of causing heat transfer by which the temperature distribution in the chamber is made uniform, the heat transfer due to air cooling generally is effected more efficiently as an amount and speed of the airflow are higher.
Accordingly, when the amount or speed of the airflow is low with respect to an amount of heat generated from a heat source, the heat radiation effect with respect to the heat source is also small. The semiconductor laser has the lowest heat resistance among elements of the optical disk, and is a heat source. Thus, to suppress a rise in temperature of the semiconductor laser is the most effective way to improve the thermal reliability and durability of the device.
According to the device disclosed in JP 8(1996)-102180 A, the airflow is formed throughout the first chamber, and thus it is a part of the airflow generated by a fan in flow amount and flow speed that reaches the semiconductor laser. With this configuration, it is less efficient in suppressing the rise in temperature of the semiconductor laser, and a sufficient heat radiation effect cannot be achieved. In this case, to increase the heat radiation effect with respect to the semiconductor laser, it is required to increase the flow amount by using a fan having a large diameter, and to increase the flow speed by increasing the rotation rate of the fan.
However, when the diameter of the fan is increased, the device becomes larger, resulting in a loss of saleability. Thus, there is a limit to the increase in the flow amount. Further, when the rotation rate of the fan is increased, the noise of the fan becomes higher, resulting in a loss of saleability. In addition, heat generation of the fan itself is increased, which reduces the heat radiation effect. Thus, there is also a limit to the increase in the flow speed.
As described above, with the configuration of JP 8(1996)-102180 A, there is a limit to the achievement of a desired heat radiation effect with respect to the semiconductor laser, and it is impossible to ensure the thermal reliability and durability of the device.
Moreover, in the device of the above-described conventional example, since the air circulation path is formed to pass through a place other than the area in which the optical disk drive is configured, the entire device becomes larger, resulting in a loss of saleability.